1. Field of the Invention
The present invention relates to dimension indicators adapted for use in sheet-metal working machine tools, namely, sheet-metal shaping, folding or shearing machine-tools. Devices of this type comprise a measuring apparatus capable of displaying the distance of the adjustment stop for positioning the metal plate or sheet on the machine in relation to a reference plane such as the folding or shearing plane.
As a rule, in a machine of the type concerned, the movement of the positioning stop member is controlled by a generally double screw-and-nut mechanism. In this case, the stop member is rigid with a pair of nuts held against rotation and engaged by a pair of rotary drive screws. Thus, it is only necessary to control the rotation of these screws in one or the other direction for moving the positioning stop member forwards or backwards, as required. To this end, one of said screws is actuatable by means of a drive motor or a manual control member, for example a crank handle, and the other screw is operatively connected to said one screw through suitable mechanical coupling means.
Under these conditions, the measuring apparatus of the dimension indicator may consist of a mechanical or electronic counter controlling the movements of rotation of one of the screws driving the positioning stop member. In this case, the drive or transmission ratio is such that the data displayed by the counter show the actual value of the movement accomplished by the positioning stop member. Of course, a calibration is required, which consists in resetting the counter when the positioning stop member lies in the reference plane corresponding in general to the sheet bending or shearing plane.
However, for technological reasons, it may become necessary to change the position of the reference plane afterwards, and this obviously involves another calibration. For instance, in plate shears the play between blades must be modified as a function of the thickness of the plate to be cut, thus making it necessary to change the position of the reference plane with respect to the stop position.
Therefore, to preserve the efficiency of the dimension indicator under all circumstances, the operator must calibrate the machine-tool each time a change occurs in the play between the blades. Now, the same problem arises in the case of a folding machine when the setting thereof is modified.